import { Observable, SubscribableOrPromise } from 'rxjs';
import { throttle as higherOrder } from 'rxjs/operators';
import { ThrottleConfig, defaultThrottleConfig } from 'rxjs/internal-compatibility';

/**
 * Emits a value from the source Observable, then ignores subsequent source
 * values for a duration determined by another Observable, then repeats this
 * process.
 *
 * <span class="informal">It's like {@link throttleTime}, but the silencing
 * duration is determined by a second Observable.</span>
 *
 * <img src="./img/throttle.png" width="100%">
 *
 * `throttle` emits the source Observable values on the output Observable
 * when its internal timer is disabled, and ignores source values when the timer
 * is enabled. Initially, the timer is disabled. As soon as the first source
 * value arrives, it is forwarded to the output Observable, and then the timer
 * is enabled by calling the `durationSelector` function with the source value,
 * which returns the "duration" Observable. When the duration Observable emits a
 * value or completes, the timer is disabled, and this process repeats for the
 * next source value.
 *
 * @example <caption>Emit clicks at a rate of at most one click per second</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks.throttle(ev => Rx.Observable.interval(1000));
 * result.subscribe(x => console.log(x));
 *
 * @see {@link audit}
 * @see {@link debounce}
 * @see {@link delayWhen}
 * @see {@link sample}
 * @see {@link throttleTime}
 *
 * @param {function(value: T): SubscribableOrPromise} durationSelector A function
 * that receives a value from the source Observable, for computing the silencing
 * duration for each source value, returned as an Observable or a Promise.
 * @param {Object} config a configuration object to define `leading` and `trailing` behavior. Defaults
 * to `{ leading: true, trailing: false }`.
 * @return {Observable<T>} An Observable that performs the throttle operation to
 * limit the rate of emissions from the source.
 * @method throttle
 * @owner Observable
 */
export function throttle<T>(this: Observable<T>,
                            durationSelector: (value: T) => SubscribableOrPromise<any>,
                            config: ThrottleConfig = defaultThrottleConfig): Observable<T> {
  return higherOrder(durationSelector, config)(this);
}
